In the process for burning lime stone (CaCO3) in the form of a lime containing mixture, also known as lime-slurry or lime-mud, to burnt lime (CaO), also denoted calcinated lime, the process equipment includes a rotary kiln modelled as a tube reactor. The lime containing mixture is introduced in one end, also denoted cold-end, of the kiln and fuel mixed with air is introduced in the other end, also denoted hot-end. The moisture of the lime containing mixture is evaporated nearly totally during the process.
The chemical process in the kiln is described as: CaCO3+heat→CaO+CO2 
A known problem for rotary kilns used for burning a lime containing mixture is the formation of rings on the inside perimeter of the kiln. Rings are formed when inert substances in the lime melt and then stick to the wall of the inside perimeter of the kiln. Rings can also be built up of evaporated substances, which condense on the inner wall closer to the cold end of the kiln. A high alkali content of the lime containing mixture is one reason for this formation and can also increase the risk of sintering. The vapour condenses at a certain temperature (position) and rings tend to form at a certain position inside the perimeter of the kiln. One or more entrenchments can be built up at the same time depending on substances present and their concentrations. Behind such a ring, a “pool” of lime is built up and a natural flow of lime through the kiln is prevented. Another known problem is that mud balls are easily formed behind such a ring, which makes the burning of lime uneven and the result of this is unevenly burnt lime, i.e. large variations in the product quality and a far from optimum use of energy. Such rings and mud balls also cause inferior lime quality and can also interrupt the production of lime. Today, ring formations inside the kiln are commonly removed by shooting them away using guns. This causes an undesired interruption in the production of burnt lime.